They're not part of the standard, but gcc, clang, and icc (Intel) support them. Alternatively, you could emit the correct instructions in an asm block on supported architectures (x86: 'jo'/'jno' for jumps, 'cmovo'/'cmovno' for conditional moves [1]) or reimplement the operations in software [2]

[1] https://www.felixcloutier.com/x86/jcc and https://www.felixcloutier.com/x86/cmovcc

[2] https://wiki.sei.cmu.edu/confluence/display/c/INT32-C.+Ensur....